1. Field
The present disclosure relates generally to switching regulators, and more particularly, to current-mode control for switching regulators.
2. Background
Voltage regulators are used to generate a constant voltage level from a supply voltage source. These voltage regulators are commonly implemented as either linear or switching regulators. A linear regulator provides closed loop control to regulate the voltage at the load. This type of regulator may be used to provide a constant voltage level which has a lower magnitude than the supply voltage source. A switching regulator is a circuit that uses an energy storage element, such as an inductor, to transfer energy from the supply voltage source to the load in discrete bursts. Feedback circuitry is used to regulate the energy transfer to maintain a constant voltage level at the load. Because the switching regulator operates to transfer energy in discrete bursts, it can be configured to step-up or step-down the voltage of the supply voltage source. A switching regulator that steps up the voltage is generally referred to as a “boost” converter and a switched regulator that steps down the voltage is generally referred to as a “buck” converter.
Switching regulators can employ either voltage-mode or current-mode control. Voltage-mode control regulators compare an compensated error voltage to a ramp to control the duty cycle of a switch that connects the supply voltage source to the storage element. The error voltage is derived from feedback circuitry that amplifies any difference between the output voltage level and a reference voltage. In contrast, current-mode control regulators use the current flowing through the switch to control the duty cycle of the switch. Two types of current-mode control regulators are commonly used today: peak current-mode and valley-current mode. For example, in a buck converter, the peak current-mode control regulator closes the switch with the rising edge of the clock and opens the switch when the peak current is sensed in the switch. A valley current-mode control regulator opens the switch with the rising edge of the clock and closes the switch when the valley current is sensed in the switch. The error voltage is used to control the peak or the valley current thresholds.
Current-mode control is considered by many to be the preferred way to regulate voltage. However, current-mode control techniques typically exhibit slow transient response due to clock latency. Another factor that limits the system bandwidth is the sampling effect, since current is only sampled once every clock cycle. Accordingly, there is a need in the art for current-mode control regulators that exhibit a better transient response.